Conventionally, a throttle control apparatus controls opening of a throttle valve to a designated opening by driving a motor corresponding to degree of stepping an accelerator pedal by a driver. Degree of stepping of the accelerator pedal is detected by an accelerator position sensor to supply current to the motor corresponding to the signal. The throttle valve driven by the motor is opened and closed to control the air intake flow to the engine.
The motor rotates the shaft of the throttle valve via a drive train such as reduction gears. The motor is accommodated in a motor case integrally molded with a throttle body rotatably supporting the shaft of the throttle valve. The motor is screwed and is fixed on the motor case at its mounting flange disposed on one end of the motor housing by mounting bolts or clamp screws. (For example, refer to Japanese Patent Application Publications No. 10-252510, and 10-131772.)
However, vibration of an engine is transmitted to the throttle body directly. Thus, components such as the motor and the gears are made to be highly rigid to endure the vibration. As shown in FIG. 6, such an assembling work is necessary that attachment of a vibration insulative leaf spring 103 between the bottom side of a motor case 104 and the opposing surface of a motor 102 by press-insertion or the like. The vibration insulative leaf spring 103 is to avoid transmitting of the engine vibration to the motor 102 via a throttle body 101.
Furthermore, on the motor housing, a motor mounting flange need to be screwed and fixed. The motor mounting flange and the motor housing are formed integrally. To acquire enough strength, the wall thickness of the motor housing is increased. As a result, the weight of the motor unit is increased. Thus, if engine vibration is transmitted to the motor, hefty load is generated. The motor vibrates intensely, thus, engagement can cause failure between a gear of a motor spindle and a reduction gear. An armature inside the motor vibrates intensely, and the motor shaft tends to fail to rotate.